On Thu, May 31, 2007 at 10:08:18PM +0200, Lars Gullik Bjønnes wrote:
> Richard Heck <[EMAIL PROTECTED]> writes:
>
> | Andre Poenitz wrote:
> | > On Thu, May 31, 2007 at 09:12:56PM +0200, Peter Kümmel wrote:
> | >
> | >>> I tried to do something like this so I didn't have the same code in two
> | >>> places:
> | >>> QModelIndex & QCitationDialog::getSelectedIndex(QListView *) {
> | >>> QModelIndexList const selIdx =
> | >>> availableLV->selectionModel()->selectedIndexes();
> | >>> if (selIdx.empty())
> | >>> return QModelIndex(); //this is an invalid one.
> | >>> return selIdx.first();
> | >>> }
> | >>> But that failed: warning: returns reference to temporary. Any ideas how
> | >>> to avoid this and still return a reference? Or could I return a smart
> | >>>
> | >> returning "const QModelIndex &" should be save. But you could also
> | >> return may value, copying QModelIndex isn't that expensive. The Qt
> | >> code return often by value, QModelIndex was designed for this.
> | >>
> | > Apart from that
> | >
> | > QModelIndex & QCitationDialog::getSelectedIndex(QListView *) {
> | > ...
> | > if (selIdx.empty())
> | > return QModelIndex(); //this is an invalid one.
> | >
> | > returns a reference to a temporary, which is useless in any case
> | > as accessing it will invoke undefined behaviour.
> | >
> | Yes, the question was how to avoid doing that and still return a
> | reference, if there is any such way.
>
> When returning by copy you could give the temporary a name to let the
> compiler use NRVO. (Optimization technique used by compilers.)
To elaborate a bit on this:
It would be somehting like
QModelIndex QCitationDialog::getSelectedIndex(QListView *) {
QModelIndex idx;
...
if (selIdx.empty()) {
idx = QModelIndex();
}
else....
return idx;
}
Andre'
PS: Note that we are talking about _GUI stuff_, not libc's strlen()
implementation ;-}
